However, because of potential high interindividual variability of factors like IL6 [51,52], further studies, e.g., with control fibroblasts from far older individuals or control fibroblasts of high passages with increased replicative senescence, need to be done to be able to better relate the severity of the PXE phenotype detected in this study to an actually aged phenotype. This evidence concerns the gene IL6 and pseudoxanthoma elasticum (inherited or acquired).